Electrical protective switch



1955 H. DIGGLE ETAL 2,720,565

ELECTRICAL PROTECTIVE SWITCH Filed Jan. 6. 1954 fnrsnfors Harold D/gg/eJohn ForY/er WK 74142;,- Their flfforzygy.

United States Patent ELECTRICAL PROTECTIVE SWITCH Hamid Biggie, Boiton,and John Fowler, Stockport, England, assignors to Metropolitau-VickersElectrical Cempany Limited, London, England, a British companyApplication January 6, 1954, Serial No. 402,518

3 Claims. (Cl. 200-114) This invention relates to an electricalprotective switch, and more particularly, this invention relates to animprovement over the transformer protective switch shown in the patentapplication of Sidney R. Smith, Jr., Serial No. 271,765, filed February15, 1952, now Patent No. 2,662,137, issued December 8, 1953, andassigned to the General Electric Company.

In said Sidney R. Smith, I r. patent application is shown a transformerprotective switch for a single phase transformer. Said switch offers theadvantage that contacts to be opened upon the occurrence of an overload,though controlled by an overload responsive element, are directly andindependently opened by a separate drive means. Said contacts arepermitted to make a predetermined number of openings and reclosingsafter which they lock open, and an external indication is provided notonly as to whether the contacts are opened or closed, but also as to thenumber of openings and reclosings that have occurred. However, as beforementioned, said transformer protective switch is designed to giveprotection to single phase electrical systems. Inasmuch as muchelectrical equipment is of the three phase type, it is desirable toprovide an electrical protective switch which can be readily utilized toprotect either single phase or plural phase electrical equipment.

Accordingly, it is an object of this invention to provide means in saidSidney R. Smith, Jr. transformer protective switch whereby said switchcan be used to protect either single phase or plural phase electricalequipment.

Our invention comprises an improved electrical protective switch for asingle or plural phase electrical system, said electrical protectiveswitch when used in a plural phase electrical system having normallyclosed contacts in each phase of said plural phase electrical system,means for opening and closing said contacts comprising a shaft biasedfor rotation in one direction, said shaft extending substantially midwaybetween the legs of a lJ-shaped escapement member substantiallyperpendicular to a plane passing through said legs, one of said legsbeing longer than the other of said legs and said longer leg having acatch notch therein substantially opposite to the upper end of saidother leg, said shaft having a crank arm thereon having a pin extendingtherefrom substantially parallel to said shaft, said U-shaped memberpivoted adjacent a base portion thereof and biased for pivotal movementin one direction whereby said catch notch is moved towards said shaftand said upper end is moved away from said shaft, said pin engaging saidnotch when said contacts are closed, an overload responsive elementpositioned in each phase of said plural phase electrical system, saidU-shaped member adapted to be pivoted in an opposite direction uponoperation of any one of said overload responsive elements wherein saidpin is disengaged from said catch notch to permit rotation of said shaftto open said contacts, said pin engaging said upper end when saidcontacts are open.

The invention will be better understood by considering the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a partly broken away exploded perspective viewof our invention in the contacts closed position. Fig. 2 is a partlybroken away sectional view of our invention in the contacts openposition, the section being taken along the line 2-2 of Fig. 1. Fig. 3is an electrical circuit diagram illustrating how our invention is usedto protect a three phase transformer apparatus.

Referring to the drawing, and more particularly to Fig. 3, illustratedtherein is a three-phase transformer 11 having a high voltage side 12and a low voltage side 13. In each of the three phases on the highvoltage side 12 there are arranged normally closed contacts 14 which areunder the control of overload-responsive elements 15 in each of thethree phases on the low voltage side 13 so that upon the occurrence ofan overload condition in any one of the three phases on the low voltageside 13 all three sets of contacts 14 will be thrown open on the highvoltage side 12.

Referring now to Fig. 1, it will be seen that a common base board 16carries on the right-hand side the high voltage contacts 14 and on theleft-hand side the low voltage control elements 15.

The high voltage contacts 14 in each phase consists of a pair of fixedcontacts 17 normally bridged by a springloaded moving contact bar orbridging member 18. Each such moving contact bar 18 is carried on theextremity of an individual insulating material switch arm 19; the threearms 19 being attached to a common rotatable shaft 26 of square crosssection carried in bearings 21 on the base 16. At its left hand end theshaft 20 has fixed to it a forked or slotted crank arm 22. Riding withina crank pin slot in the arm 22 is a pin 23 carried by a crank arm 24which in turn is fixed on a rotatable shaft 25. It will be seen thatwith the crank arm 24 occupying the position as shown in Fig. l thecontacts 17-13 are held closed, but that if the shaft 25 is made torotate counterclockwise then during one complete rotation the switchcontacts 17-18 will be caused to execute an opening and reclosingmovement once. See also Fig. 2.

For the purpose of effecting such counterclockwise rotation of the shaft25', a small pinion 26 fixed upon the left hand end of shaft 25 mesheswith a large pinion 27 which under the pressure of a multi-turn torsionspring 28 tends to rotate in a clockwise direction. A shaft 29 extendsfrom the pinion 27 and spring 28 through the side wall 3% of atransformer tank, not shown, to a combined indicator finger and resetlever 31 which is rotatable over the surface of a dial plate 32.

Thus, when the spring 28 is permitted to cause rotation of the shaft 25and crank arm 24, partial rotation in opposite directions is imparted toshaft 21). Rotation of shaft 25 is permitted by an escapement mechanismassociated with the overload responsive elements now to be described.

Fixed upon the shaft 25 is a crank arm 33 carrying a pin 34 which in therotation of shaft 25 moves in the path of a U-shaped escapement member35 which is urged in a counterclockwise direction about its pivot shaft36 by means of a torsion spring 37. In the position shown in Fig. 1 andcorresponding to ciosure of contacts 14, the pin 34 is up against acatch notch on the right hand limb of the escapement member 35; whileupon movement of the escapement member 35 clockwise, the pin 34 isreleased and a counterclockwise movement of the shaft 25 is permitteduntil the pin 34 is brought up against the upper extremity of the lefthand limb of the escapement member 35. In this position, almostdiametrically opposite from the former, the contacts 14 are open as isindicated in Fig. 2.

The means by which clockwise displacement of the escapement member 35 isbrought about consists of three bimetallic strips 38 which are theelements most nearly to be identified with the overload responsiveelements 15 of Fig. 3, that is to say, each one is arranged in one phaseon the low voltage side 13, the circuit passing from terminal 39, overthe bimetal strip 38 and a flexible connector 40, to the terminal 41.The strip 38 is mounted with its upper end fixed in the terminal 39 andwith its lower end free to flex towards the longer leg portion ofescapement member 35 as the strip becomes heated. The longer notched legportion of the escapement member 35 carries a cross piece 4-2 withinwhich are three adjustment screws 43 against which the free end of abimetal strip 38 bears when the strip is sufficiently flexed upon anoverload.

By reason of the step-down gearing 26, 27 between the shaft 25 and theshaft 29, each half-rotation of the shaft 25, from contacts closed tocontacts open, or from open to closed, results in a one-eighth rotationof indicator 31. The sequence of opening and closing can occur threetimes, upon a fourth opening a stop pin 44 on the pinion 27 will havecome to rest against the under side of one of the bearings 45 for theshafts 25 and 29, and the switch will remain locked out. To reset theswitch the indicator and reset lever 31 is turned back counterclockwiseto its original position, thus winding up the spring 28 and closing thecontacts 14.

While there has been shown and described a particu lar embodiment of theinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention, andthat it is intended by the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electrical protective switch for three phase electrical apparatuscomprising three pairs of spaced stationary electrically conductivecontacts, three movable switch arms, each of said arms carried at oneend thereof by a rotatable shaft, the other ends of said arms having anelectrically conductive bridging contact member thereon, said bridgingcontact members adapted to span each of said pairs of spaced contacts tocomplete an electrical circuit therebetween, said shaft having a slottedcrank arm connected at one end thereof to said shaft, the other end ofsaid slotted crank arm having a crank pin slot therein, anotherrotatable shaft for imparting motion to said switch arm carrying shaft,said another rotatable shaft having a crank arm connected at one endthereof to said another rotatable shaft, said crank arm having a pinprojecting from another end thereof substantially parallel to the axisof said another shaft, said pin positioned within said crank pin slot,means continuously t urging said another rotatable shaft for rotation inone direction, means for alternately releasing said another rotatableshaft for rotation in said one direction and for restraining saidanother rotatable shaft from rotation whereby said bridging contactmembers alternately disengage and engage said pairs of stationarycontacts comprising a U-shaped escapement member, said U-shaped memberhaving one leg thereof longer than the other leg thereof, said one leghaving a catch notch therein disposed approximately opposite to theupper end of said other leg, said another rotatable shaft extendingsubstantially normal to a plane passing through the legs of saidU-shaped member and aligned approximately midway of said upper end andcatch notch, said another rotatable shaft having another crank armconnected at one end thereof to said another rotatable shaft, saidanother crank arm having a pin extending from another end thereofsubstantially parallel to said another shaft, said another crank arm pinalternately engageable with said catch notch and upper end to retainsaid bridging contact members engaged and disengaged with said pairs ofstationary contacts, said Ushaped member pivoted adjacent a base portionthereof and means continuously urging said U-shaped member for pivotalmovement in one direction whereby said catch portion lies in the path ofmovement of said another crank arm pin, said one ,leg having a crosspiece thereon extending substantially normal to said plane, threeelectrically conductive bimetallic elements, each of bimetallic elementsadapted for connection in one phase of said three phase electricalapparatus and each of said pairs of stationary contacts adapted forconnection in one phase of said three phase electrical apparatus, eachof said bimetallic elements adapted for movement towards said crosspiece to pivot said U- shaped member in another direction whereby saidupper end lies in the path of movement of said another crank arm pin.

2. An electrical switch comprising a rotatable shaft, a plurality ofswitch arms carried by said shaft, said switch arms connected at one endthereof to said shaft, the other ends of said switch arms having anelectrically conductive bridging contact member thereon, each of saidbridging contact members adapted to engage and disengage a pair ofspaced stationary electrically conductive contacts upon partial rotationof said shaft in opposite directions, means for imparting partialrotation to said shaft in opposite directions comprising anotherrotatable shaft continuously urged for rotation in one direction, saidanother shaft having a crank arm connected at one end thereof to saidanother shaft, another end of said crank arm having a pin projectingtherefrom substantially parallel to said another shaft, a slotted crankarm connected at one end thereof to said switch arm carrying shaft, theother end of said slotted crank arm having a crank pin slot therein,said another shaft crank arm pin positioned in said crank pin slot, andmeans for alternately permitting and prohibiting rotation of saidanother shaft comprising another crank arm carried at one end thereof bysaid another shaft, another end of said another crank arm having a pinextending therefrom substantially parallel to said another shaft, apivotally mounted U-shaped escapement member having two leg portions anda base portion, one of said leg portions being longer than the other ofsaid leg portions, said longer leg portion having a catch notch thereinsubstantially opposite to the upper end of said other leg portion, saidanother shaft extending between said leg portions approximately normalto a plane passing through the leg portions of said U-shaped member andapproximately midway of said upper end and catch notch whereby saidanother crank arm pin will alternately engage said catch notch and upperend upon pivotal movement of said U-shaped member in oppositedirections, said U-shaped member pivoted adjacent said base portion andcontinuously urged for pivotal move ment in one direction whereby saidupper end lies without the path of movement of said another crank armpin and said catch notch lies in said path of movement for engagement ofsaid catch notch and another crank arm pin whereby said bridging contactmembers and pairs of stationary contacts are retained in engagedrelationship, and means for pivoting said U-shaped member in an oppositedirection comprising a cross piece carried by said longer leg portionand extending substantially parallel to said another shaft, and aplurality of electrically conductive bimetallic elements, each of saidelements adapted to abut said cross piece and pivot said U-shaped memberin an opposite direction whereby said catch portion lies without thepath of movement of said another crank arm pin and said upper end liesin said path of movement whereby said upper end and another crank pinengage to retain said bridging contact members and pairs of spacedcontacts disengaged.

3. An electrical switch comprising a pair of spaced stationaryelectrically conductive contacts, a switch arm carried at one endthereof by a rotatable shaft, an elec- 5 trically conductive bridgingcontact member carried by another end of said switch arm adapted toengage and disengage said pair of contacts upon partial rotation of saidshaft in opposite directions, another shaft continuously urged forrotation in one direction for imparting partial rotation to said switcharm carrying shaft in opposite directions, said another shaft having acrank arm connected at one end thereof to said another shaft, anotherend of said crank arm having a pin thereon extending substantiallyparallel to said another shaft, a slotted crank arm connected at one endthereof to said switch arm carrying shaft, another end of said slottedcrank arm having a crank pin slot therein, said another shaft crank armpin protruding into said crank pin slot, means for alternatelypermitting and prohibiting rotation of said another shaft to alternatelyengage and disengage said bridging contact member and pair of contactscomprising a U-shaped escapement member having two leg portions and abase portion, said another shaft extending between said leg portionssubstantially normal to a plane passing through said leg portions, saidU-shaped member pivoted adjacent said base portion for pivotal movementin opposite directions, one of said leg portions being longer thananother of said leg portions, said longer leg portion having a catchnotch therein approximately opposite to an upper end of said another legportion, said another shaft positioned substantially midway of saidupper end and catch notch, means continuously urging said U-shapedmember for pivotal movement in one direction whereby said catch notch ismoved towards said another shaft and said upper end is moved away fromsaid another shaft, an electrically conductive bimetallic elementadapted to be moved from an out of contact position with respect to saidlonger leg portion towards said longer leg portion for abutmenttherewith wherein said U-shaped member is pivoted in an oppositedirection whereby said catch notch is moved away from said another shaftand said upper end is moved toward said another shaft, said anothershaft having another crank arm connected at one end thereof to saidanother shaft, another end of said another crank arm having a pinextending therefrom substantially parallel to said another shaft adaptedto alternately abut said catch notch and upper end to alternately retainsaid bridging contact member engaged and disengaged with said pair ofcontacts.

Jackson Sept. 15, 1953 Alter Apr. 6, 1954

